1. Field of the Invention
The present invention relates to a thickened acid cleaner composition formed for facilitating subsequent treatment of the composition after use, and a method of treating the used cleaning composition to remove solids and entrained matter having a high biological oxidation demand.
2. Description of the Prior Art
Use of acid in cleaning compositions is known, for instance, U.S. Pat. No. 2,257,467 discloses a solidified acid composition for cleaning toilet bowls and the like wherein the composition consists of sodium silicate, water and hydrochloric acid. Another acid cleaner is disclosed in U.S. Pat. No. 3,271,319 wherein it is taught that stains can be removed from glass surfaces by the use of an acid cleaner consisting of water, hydrofluoric acid, a carboxymethylcellulose thickener and a small amount, usually less than 1 percent, of an alkyl sulfate or alkyl aryl sulfonate wetting agent. A still more recent patent, U.S. Pat. No. 3,622,391, teaches removing aluminide coatings from cobalt base or nickel base superalloys by the use of a hydrofluoric acid and water composition which permissably includes a low foaming or nonfoaming wetting agent.
Mineral acids have also been used in cleaning compositions as a defoamer. This technique is illustrated in U.S. Pat. No. 3,650,965 wherein the foaming qualities of nonionic surfactants for food industry cleaning can be reduced by the use of an organic acid coupled with a mineral acid such as phosphoric acid, the acid component being more than the surfactant component.
It has also been known to clean transportation equipment such as trains, boxcars and the like by the use of an acid cleaner to remove siliceous soils, followed by an alkaline cleaner to remove organic and oily soils, then finally followed by water rinsing. An especially good acid cleaner which is effective in cleaning vehicles such as railroad cars and locomotives is disclosed in U.S. Pat. No. 3,793,221.
It is well known that the use of cleaning compositions provides a waste water which may cause a disposal problem. This is particularly true when acid cleaners or the like are to be utilized. With the special emphasis now being made with respect to environmental protection, effective treatment of such wastes prior to disposal is positively essential.
In accordance with the usual procedures, waste treatment processes are adapted to remove suspended solids and reduce biological oxidation demand from the waste water prior to discharge or re-use of the water. In a typical operation, the waste water is treated with additives to assist in flocculation and subsequent filtration, sedimentation or floatation. However, a problem has been encountered in connection with the addition of flocculent, because accurate determination of the amount to be added varies with the washing process and needs to be measured when using the cleaner compositions of the prior art. In addition, heavy surges of waste water from batch type washing operations sometimes exceeds the capacity of the waste treatment facility.